runtime checks for socket access in async functions

[SteffenDE]

Followup for #3160.

[josevalim]

You can probably use eval_quoted. The if false is because we want the code expanded but not executed. :)

Suggested change

	defmodule AssignAsyncSocket do
	use Phoenix.LiveView
	def mount(_params, _session, socket) do
	{:ok, #{unquote(fun)}(socket, :foo, fn ->
	do_something(socket.assigns)
	end)}
	end
	defp do_something(_socket), do: :ok
	end
	require Phoenix.LiveView
	if false do
	Phoenix.LiveView.#{unquote(fun)}(socket, :foo, fn ->
	do_something(socket.assigns)
	end)
	end

[SteffenDE]

No luck with eval_quoted.

ExUnit.start()

defmodule MyTest do
  use ExUnit.Case

  import ExUnit.CaptureIO

  for fun <- [:assign_async, :start_async] do
    test "warns when passing socket to #{fun} function" do
      warnings =
        capture_io(:stderr, fn ->
          Code.eval_quoted(
            quote bind_quoted: [fun: unquote(fun)] do
              require Phoenix.LiveView

              if false do
                fun(socket, :foo, fn ->
                  do_something(socket.assigns)
                end)
              end
            end
          )
        end)

      assert warnings =~
               "you are accessing the LiveView Socket inside a function given to #{unquote(fun)}"
    end
  end
end

mix run test.exs


  1) test warns when passing socket to start_async function (MyTest)
     test.exs:9
     ** (CompileError) nofile: cannot compile file (errors have been logged)
     stacktrace:
       (elixir 1.16.1) src/elixir_clauses.erl:45: :elixir_clauses.clause/6
       (elixir 1.16.1) src/elixir_clauses.erl:347: anonymous fn/7 in :elixir_clauses.expand_clauses_origin/6
       (stdlib 5.2) lists.erl:1706: :lists.mapfoldl_1/3
       (stdlib 5.2) lists.erl:1707: :lists.mapfoldl_1/3
       (elixir 1.16.1) src/elixir_clauses.erl:351: :elixir_clauses.expand_clauses_origin/6
       (stdlib 5.2) lists.erl:1706: :lists.mapfoldl_1/3
       (elixir 1.16.1) src/elixir_clauses.erl:98: :elixir_clauses.case/4
       (elixir 1.16.1) src/elixir_expand.erl:692: :elixir_expand.expand_case/5
       (elixir 1.16.1) expanding macro: Kernel.if/2
       nofile:1: (file)



  2) test warns when passing socket to assign_async function (MyTest)
     test.exs:9
     ** (CompileError) nofile: cannot compile file (errors have been logged)
     stacktrace:
       (elixir 1.16.1) src/elixir_clauses.erl:45: :elixir_clauses.clause/6
       (elixir 1.16.1) src/elixir_clauses.erl:347: anonymous fn/7 in :elixir_clauses.expand_clauses_origin/6
       (stdlib 5.2) lists.erl:1706: :lists.mapfoldl_1/3
       (stdlib 5.2) lists.erl:1707: :lists.mapfoldl_1/3
       (elixir 1.16.1) src/elixir_clauses.erl:351: :elixir_clauses.expand_clauses_origin/6
       (stdlib 5.2) lists.erl:1706: :lists.mapfoldl_1/3
       (elixir 1.16.1) src/elixir_clauses.erl:98: :elixir_clauses.case/4
       (elixir 1.16.1) src/elixir_expand.erl:692: :elixir_expand.expand_case/5
       (elixir 1.16.1) expanding macro: Kernel.if/2
       nofile:1: (file)


Finished in 0.01 seconds (0.01s on load, 0.00s async, 0.00s sync)
2 tests, 2 failures

Randomized with seed 369048

“errors have been logged”

[josevalim]

What about:

          Code.eval_quoted(
            quote do
              require Phoenix.LiveView

              if false do
                unquote(fun)(socket, :foo, fn ->
                  do_something(socket.assigns)
                end)
              end
            end

[josevalim]

Actually, sorry:

        Code.eval_quoted(
            quote do
              require Phoenix.LiveView

              if false do
                Phoenix.LiveView.unquote(fun)(socket, :foo, fn ->
                  do_something(socket.assigns)
                end)
              end
            end

[SteffenDE]

Nope. No luck with that either. But I know why I get no compiler errors... It's inside the capture_io.

Removing it yields

error: undefined variable "socket" (context MyTest)
└─ nofile:1

which kind of makes sense.

Besides that I think the defmodule code is actually alright. Might even be better to understand.

[SteffenDE]

I added some eval_quoted variants as well. Let me know which ones you like better.

[SteffenDE]

c80b583

[chrismccord]

❤️❤️❤️🐥🔥